Inherited differences in human's ability to taste bitter thiourea compounds, specifically phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP), have been studied since 1931. 70% of adults and children in the U.S. are "tasters" of these compounds and 30% are "non-tasters." Researchers have found that tasters and non-tasters differ in their food preferences, selection, and body weights. However, unanswered questions remain, particularly about the relationship between taste and obesity in children. This year (2003) marked the discovery of the gene responsible for the ability to taste PTC, and with this discovery, many of the previously unanswered questions can now be given empirical attention. The long-term goals of this research are 1) to characterize the relationship between taste and food intake, 2) to determine if associations between taste and body weight in children will track into adulthood, 3) to elucidate the behavioral mechanisms of positive energy balance in PROP non-tasters, and 4) to determine the associations between PTC haplotypes, mechanisms of positive energy balance, and body composition in children. The general hypotheses behind this work are: 1) genes influence taste perception, 2) changes in taste perception influence both response to and selection of energy density within a single meal, and 3) sustained, uncompensated, changes in energy density in the diet ultimately alter body weight. To test these hypotheses, we propose a two part study. Part I will test 75,4-6 y. old children, half boys and half girls. In part I, we will validate a novel training protocol that can be used to classify children's ability to taste PROP. In Part II, we propose to test 120,4-6 y. old boys and girls, to test the hypothesis that PROP non-tasters select higher energy dense foods, eat more when exposed to higher energy dense meals, and have higher body weights and levels of body fat. The long-term goal of this work is to train the candidate to become an independent investigator who will compete for future award programs (e.g., R01s, R03s) .